Historical sketch on Immunity 533 



obtained, in animals well immunised against the cholera vibrio, 

 a serum endowed with a high anti-infective power but entirely with- 

 out any antitoxic property. The guinea-pigs themselves, very resistant 

 to the cholera peritonitis, were found, on the other hand, to be very 

 susceptible to the minimum lethal dose of the cholera poison. The 

 absence of antitoxic power in the fluids of the body taken in con- 

 nection with a well-marked phagocytic reaction in a large number 

 of cases of immunity, natural and acquired, has turned the scale in 

 favour of the cellular theory. The impossibility on the part of those 

 who maintain the purely bactericidal theory of the body fluids, to reply 

 to the objections above mentioned has accentuated this favourable 

 movement. Just at this moment, when the theory of phagocytes might 

 be regarded to have obtained the rights of citizenship, a discovery was 

 made which appeared to overturn it completely. I have mentioned 

 more than once that the attempts of the partisans of the bactericidal 

 theory of the body fluids have failed whenever it was necessary to 

 give evidence of their action in the refractory animal. Instead of a 

 destruction of the micro-organisms in these fluids, it was always found 

 that they perished inside the phagocytes. These facts have even led 

 to the manifestation of a desire to harmonise the humoral theory 

 with the theory of phagocytosis. Denys, with certain of his colla- 

 borators, and Buchner and his pupils came to the conclusion that [5571 

 the alexins are merely leucocytic products. As regards the theory 

 of phagocytosis we have this section, who attribute an important 

 function in healing and immunity to the emigration of the leucocytes 

 towards, and their accumulation at the menaced spot. They admit 

 that the leucocytes really represent the healing elements of the animal 

 body ; it is not, however, they say, their phagocytic functions which 

 confer upon them this role but their power of secreting alexin. These 

 bactericidal substances act outside the phagocytes in the plasmas 

 of the blood and of the exudations and phagocytosis only intervenes 

 at a later period and secondarily. 



This new modification of the bactericidal theory of the body fluids j 

 has often been termed by Buchner a connecting bridge between the \ 

 humoral theory and the cellular theory of immunity. 



In the midst of this movement of conciliation, Pfeiffer 1 in 1894 

 published a work on the immunity of the guinea-pig against 

 experimental cholera peritonitis. He maintains that here the 



1 Ztschr. f. Hyg., Leipzig, 1894, Bd. xvin S. 1; c also Pfeiffer u. Issaeff, ibid., 

 1894, Bd. XVII, S. 355. 



